Performance evaluation of 3D printed miniature electromagnetic energy harvesters driven by air flow

As a renewable and non-polluting energy source, wind is used to produce electricity via large-diameter horizontal or vertical axis wind turbines. Such large wind turbines have been well designed and widely applied in industry. However, little attention has been paid to the design and development of miniature wind energy harvesters, which have great potential to be applied to the HVAC (heating, ventilating and air conditions) ventilation exhaust systems and household personal properties. In this work, 10 air-driven electromagnetic energy harvesters are fabricated using 3D printing technology. Parametric measurements are then conducted to study the effects of (1) the blade number, (2) its geometric size, (3) aspect ratio, presence or absence of (4) solid central shaft, (5) end plates, and (6) blade orientation. The maximum electrical power is 0.305 W. To demonstrate its practical application, the electricity generated is used to power 4 LED (light-emitting diode) lights. The maximum overall efficiency ηmax is approximately 6.59%. The cut-in and minimum operating Reynolds numbers are measured. The present study reveals that the 3D printed miniature energy harvesters provide a more efficient platform for harnessing ‘wind power’.

Human passive motions and a user-friendly energy harvesting system

Energy harvesting for wireless sensors and consumer electronic devices can significantly improve reliability and environmental sustainability of the devices. This is achieved by eliminating the dependency of these devices on rechargeable batteries, using clean and/or renewable energy sources. Energy harvesting from various energy sources is widely discussed among researchers and entrepreneurs, including harvesting energy from microscale phenomena. This topic is receiving increasing attention due to the rising numbers of low-power consumer electronic devices and wireless sensors, but also the increasing demand for more convenient and available devices. This article presents a feasibility study for an energy harvesting system based on a human's breathing motion. The system is based on a modified pants belt that is integrated with an array of piezoelectric films and a harvesting circuit. The proposed energy harvester generates electricity from reciprocal abdominal motions of the human subject. In comparison with existing breathing-based energy harvesters, the proposed system allows for safe and convenient energy harvesting with no influence on the natural movement of the lungs. Stomach pressure analysis and measurement, as well as the design and simulations of the proposed harvester, are presented. © 2013 The Author(s).

Robust mechanical-to-electrical energy conversion from short-distance electrospun poly(vinylidene fluoride) fiber webs

Electrospun polyvinylidene fluoride (PVDF) nanofiber webs have shown great potential in making mechanical-to-electrical energy conversion devices. Previously, polyvinylidene fluoride (PVDF) nanofibers were produced either using near-field electrospinning (spinning distance < 1 cm) or conventional electrospinning (spinning distance > 8 cm). PVDF fibers produced by an electrospinning at a spinning distance between 1 and 8 cm (referred to as "short-distance" electrospinning in this paper) has received little attention. In this study, we have found that PVDF electrospun in such a distance range can still be fibers, although interfiber connection is formed throughout the web. The interconnected PVDF fibers can have a comparable β crystal phase content and mechanical-to-electrical energy conversion property to those produced by conventional electrospinning. However, the interfiber connection was found to considerably stabilize the fibrous structure during repeated compression and decompression for electrical conversion. More interestingly, the short-distance electrospun PVDF fiber webs have higher delamination resistance and tensile strength than those of PVDF nanofiber webs produced by conventional electrospinning. Short-distance electrospun PVDF nanofibers could be more suitable for the development of robust energy harvesters than conventionally electrospun PVDF nanofibers.

Applications of electrospun nanofibers for electronic devices

In recent decades, electrospinning of nanofibers has progressed very rapidly in both scientific and technological aspects, and electrospun nanofibers have shown enormous potential for various applications. In particular, electrospun nanofibers have significantly enhanced the application performance of many electronic devices, such as solar cells, mechanical-to-electric energy harvesters, rechargeable batteries, supercapacitors, sensors, field-effect transistors, diodes, photodetectors, and electrochromic devices. This chapter provides a comprehensive summary on the recent progress in the application of electrospun nanofibers in electronic devices.

Simulation of a novel piezoelectric energy harvester

This paper focuses on a novel piezoelectric energy harvester for nanofiber PVDF to capture energy from vibration environment. A Resembling CMOS(R-CMOS) circuit consisting of two pMOS transistors and two nMOS transistors is presented, which can greatly increase the energy efficiency and reduce the power dissipation tremendously. Meanwhile, the novel harvester supplies smooth direct current. Simulation result of MULTISIM has shown that by using this novel piezoelectric energy harvester the input voltage (5v) can be rectified to be an output voltage (4.24v). The voltage conversion rate of the novel harvester is as high as 84.8% which is much larger than the rate of traditional rectifier circuit. Its potential application is in micro sensors, wireless transducers, and sensor networks.

Numerical investigation of the turbulent energy budget in the wake of freely oscillating elastically mounted cylinder at low reduced velocities

We present a numerical study of the turbulent kinetic energy budget in the wake of cylinders undergoing Vortex-Induced Vibration (VIV). We show three-dimensional Large Eddy Simulations (LES) of an elastically mounted circular cylinder in the synchronization regime at Reynolds number of Re=8000. The Immersed Boundary Method (IBM) is used to account for the presence of the cylinder. The flow field in the wake is decomposed using the triple decomposition splitting the flow variables in mean, coherent and stochastic components. The energy transfer between these scales of motions are then studied and the results of the free oscillation are compared to those of a forced oscillation. The turbulent kinetic energy budget shows that the maximum amplitude of VIV is defined by the ability of the mean flow to feed energy to the coherent structures in the wake. At amplitudes above this maximum amplitude, the energy of the coherent structures needs to be fed additionally by small scale, stochastic energy in form of backscatter to sustain its motion. Furthermore, we demonstrate that the maximum amplitude of the VIV is defined by the integral length scale of the turbulence in the wake